Effects of Transition Metals on Metal–Octaaminophthalocyanine-Based 2D Metal–Organic Frameworks

Abstract

Metal−octaaminophthalocyanine (MOAPc)based 2D conductive metal−organic frameworks (cMOFs) have shown great potential in several applications, including sensing, energy storage, and electrocatalysis, due to their bimetallic characteristics. Here, we report a detailed metal substitution study on a family of isostructural cMOFs with Co 2+ , Ni 2+ , and Cu 2+ as both the metal nodes and the metal centers in the MOAPc ligands. We observed that different metal nodes had variations in the reaction kinetics, particle sizes, and crystallinities. Importantly, the electronic structure and conductivity were found to be dependent on both types of metal sites in the 2D cMOFs. Ni-NiOAPc was found to be the most conductive one among the nine possible combinations with a conductivity of 54 ± 4.8 mS/cm. DFT calculations revealed that monolayer Ni-NiOAPc has neither the smallest bandgap nor the highest charge carrier mobility. Hence its highest conductivity stems from its high crystallinity. Collectively, these results provide structure property relationships for MOAPc-based cMOFs with amino coordination units.

Tuning Two-Dimensional Phthalocyanine Dual Site Metal–Organic Framework Catalysts for the Oxygen Reduction Reaction

“…All the phthalocyanine-based MOFs were prepared following our reported procedures. 29 Briefly, the homemade metal(II) 2,3,9,10,16,17,23,24-octaamino-phthalocyanine ligands (5 mg, 5 μmol) were dispersed in 3.5 mL dimethylformamide (DMF) or dimethylacetamide (DMA). The corresponding transition-metal (Co 2+ /Ni 2+ /Cu 2+ , 15 μmol) nitrates were dissolved in 0.75 mL sodium acetate (NaOAc) aqueous solution (1.6 M) and 1.5 mL DMF or DMA and then added into the ligand solution.…”

“…This square-planar coordination was found to enable excellent electron delocalization through continuous conjugation and long-range electron conductivity in the MOFs. 29 The metal nodes in these 2D MOFs provide different types of M−N 4 sites from the ligands, in which the N atoms are from two amino radicals (−NH • ) and two azanides (−NH − ). Typically, metal nodes are more flexible due to the presence of a smaller amino/azanide moiety as compared to bulk phthalocyanine in metal ligands.…”

“…An AA-eclipsed stacking model is used for the 2D MOF layers, as is suggested in our previous work. 29 The phthalocyanine-based ligand (with a metal site in the center, M2) and a metal node (M1) can be clearly seen from the model, with each metal site coordinated with four nitrogen atoms (M−N 4 structure). Structurally, M2 sites are electron poor and less covalently bonded with neighboring nitrogens than are the M1 sites.…”

“…Previously reported TEM images of the as-synthesized Co− Cu MOF indicate a tetragonal unit cell with square pores' side length of ∼1.8 nm. 29 The Brunauer−Emmett−Teller (BET) surface areas of the MOFs are in the range of 119 (Co−Co) to 548 (Co−Cu) m 2 g −1 , suggesting decent crystallinity and porosity. 29 There are differences in the crystallinity of the MOF family as their crystal domain sizes vary from 7.4 to 12.3 nm (excluding Co−Co).…”

“…29 The Brunauer−Emmett−Teller (BET) surface areas of the MOFs are in the range of 119 (Co−Co) to 548 (Co−Cu) m 2 g −1 , suggesting decent crystallinity and porosity. 29 There are differences in the crystallinity of the MOF family as their crystal domain sizes vary from 7.4 to 12.3 nm (excluding Co−Co). Co−Co is an amorphous MOF material (no ordered crystallites).…”